In the anatomy of the human heart, the left atrium receives oxygenated blood from the lungs through the pulmonary veins. The mitral valve separates the left atrium from the left ventricle. The mitral annulus comprises a fibrous ring encircling the orifice between the left atrium and the left ventricle. The mitral valve is a bicuspid valve having a posterior leaflet that cooperates with an anterior leaflet. During diastole, as the contraction triggered by the sinoatrial node progresses through the atria, oxygenated blood passes through the mitral valve into the left ventricle. In this phase, the aortic valve leading into the ascending aorta closes, allowing the left ventricle to fill with blood. A similar flow of venous blood occurs from the right atrium through the pulmonary valve to the right ventricle. Once the ventricles are full, they contract during the systolic phase and pump blood out of the heart. During systole, the mitral valve closes and the aortic valve opens, thus preventing blood from regurgitating into the left atrium and forcing blood into the aorta, and from there throughout the body. Because of the high pressures associated with the left ventricle during systole, proper functioning of the mitral valve to prevent blood from flowing back through the system is extremely important.
In many developed countries, congestive heart failure is a leading cause of hospitalization and death, and its incidence is increasing. When imperfections in the mitral valve allow blood to flow backward into the left atrium, known as mitral regurgitation, the left ventricle must pump progressively harder to circulate blood throughout the body, which in turn promotes congestive heart failure. Heart transplantation is considered a standard treatment for select patients with severe congestive heart failure and end-stage heart disease, but only a small number of donor hearts are available and there are severe surgical risks for weaker patients. Accordingly, alternative medical and surgical strategies are evolving to treat such conditions.
One typical cause of mitral regurgitation is malformation of the mitral annulus, such as due to dilation of the left ventricle. Malformation of the mitral annulus can cause the mitral leaflets to not coapt properly, thereby allowing blood to flow back into the left atrium. Stabilizing and restructuring the mitral annulus can allow the mitral leaflets regain their proper function and eliminate or reduce mitral regurgitation.
Various interventions have been used to alter the size and shape of the regurgitant orifice area. Annuloplasty rings have been developed in various shapes and configurations over the years to correct mitral regurgitation and other conditions which reduce the functioning of the valve. For example, Carpentier, et al. in U.S. Pat. No. 4,055,861 disclosed two semi-rigid supports for heart valves, one of which being closed (or D-shaped) and the other being open (or C-shaped). Some annuloplasty rings are contoured to conform to an abnormal posterior aspect, or other portion, of the mitral annulus, such as is disclosed by McCarthy in U.S. Pat. No. 7,608,103. A variety of other styles of annuloplasty rings are also known.
Typically, annuloplasty rings, regardless of the style, are implanted via open heart surgery through the left atrium and are fixed to the mitral annulus or surrounding tissue with a plurality of sutures disposed radially around the perimeter of the ring and attached to a sewing sheath surrounding the ring. The sutures typically pull the mitral annulus radially inwardly toward the ring to reduce the diameter and/or reshape the mitral annulus.